There are approximately 10 million wearers of prosthetic joints in the world today, and the number of prosthetic joint surgeries continues to increase each year, mainly because of population aging and of the increasing prevalence of obesity, which leads to an excess weight borne by the joints. Accordingly, it is estimated that by 2020, 2.5 million individuals will undergo surgery to insert a prosthetic joint or to replace an existing prosthetic joint. Besides, an increase in the number of initial joint replacements done in young patients (i.e. under 50 years old) is also observed. Current figures indicate that approximately 430,000 total hip and knee replacements are done each year in the United States, while approximately 130,000 total hip replacements (THR) and 100,000 total knee replacements (TKR) are implanted or replaced each year in France, where there are currently more than one million wearers of prosthetic joints.
Infection is one of the main complications of joint replacement surgery. In spite of the considerable progress recorded over recent years, prosthetic joint infections are still common, hovering between 0.3% and 2% for total hip replacements, and between 0.5% and 5% for total knee replacements, with the highest rates of infection occurring when existing prosthetic joints are replaced (from 3 days to nearly 20 years following surgery, with an average of 20% of infections occurring within 3 months of joint replacement; 40% occurring between 3 months and 2 years; and 40% occurring after 2 years). These infections are associated with a non-negligible mortality rate (2.5%) as well as with a high morbidity. They usually require one or several additional surgeries and a long course of antibiotics, resulting in significant and often lengthy functional disability. Eventually, the cost of managing these complications is very high, estimated at approximately 60,000 euros per prosthetic joint infection, thereby multiplying by four the cost price of a prosthetic joint when an infection occurs, e.g. reaching a total cost of approximately 80,000 euros for an infected prosthetic hip joint.
Prosthetic joints become infected by two different pathogenetic routes: locally introduced and hematogenous types of osteomyelitis. The locally introduced form of infection is the result of wound sepsis contiguous to the prosthesis or operative contamination. Any bacteremia can induce infection of a total joint replacement by the hematogenous route. Genitourinary and gastrointestinal tract procedures or infections are associated with gram-negative bacillary, Enterococci and anaeobic infections of prostheses. The frequency of the presence of the specific etiologic microorganisms in prosthetic joint sepsis varies among the published studies, but a general view of the spectrum of this bacteriology and the prominence of certain microbial groups is known. Staphylococci (coagulase-negative staphylococci and S. aureus) are the principal causative agents; aerobic streptococci and gram-negative bacilli are each responsible for 20% to 25%, and anaerobes represent 10% of these infections. Recent study reported microbiologic findings of 53 episodes of gram-negative prosthetic joint infections occurring among patients treated during 2000-2006 with 19% of Pseudomonas aeruginosa, 10% Escherichia coli, 8% Klebsiella pneumoniae, 3% Enterobacter cloacae, 2% Acinetobacter baumannii, 2% Salmonella enterica, 2% Haemophilus influenzae, 1% Proteus mirabilis, 1% Bacteroides fragilis and 3% non identified for monomicrobial infections (Hsieh et al. (2009) Clin. Infect. Dis. 49: 1036-1043). Other prosthetic joint infections due to other gram-negative bacteria such as Morganella morganii, Pasteurella multocida, Serratia marcescens, Brucella spp., Francisella tularensis, Neisseria elongata, Neisseria perflava, Citrobacter koseri, Yersinia enterolitica were also reported [Navarro et al. (1997) J. Infect. 35: 192-194; Arslan et al. (1998) J. Infect. 37: 70-71; Pittman et al. (1996) Pediatr. Neurosurg. 24: 50-51; Cooper et al. (1999) Clin. Infect. Dis. 29(6): 1589-1591; Evans et al. (2007) J. Med. Microbiol. 56(Pt 6): 860-862; Clark et al. (1968) Annals of Internal Medicine 68: 2386-2389; Adam et al. (2010) The journal of arthroplasty in press; Pras et al. (1992) Postgrad. Med. J. 68(803): 762-763; Werno et al. (2002) J. Clin. Microbiol. 40(3): 1053-1055; Peterson et al. (1993) Clin. Infect. Dis. 16(3): 439-440)]. The spectrum of microbial agents capable of causing prosthetic joint infection is however unlimited and even includes organisms ordinarily considered “contaminants” of cultures, such as Bacillus spp.
Although gram-negative infections constitute a relatively minor proportions of prosthetic joint infections, they are of significant clinical importance, because treatment of such infections is considered more complicated as a result of virulence of the organisms, their growing resistance to antimicrobial agents, and the comorbid conditions of patients (McDonald et al. (1989) J. Bone Joint Surg. Am. 71: 828-834; Legout et al. (2006) Clin. Microbiol. Infect. 12: 1030-1036; Schurman et al. (1978) Clin. Orthop. Relat. Res. 134: 268-274).
The gold standard for diagnosing prosthesis infection remains bacteriological analysis, which involved isolation and culture of the infecting bacteria at the site of infection, from relevant samples. Bacteriological analysis is generally considered as significant if at least 2 joint aspirate or intraoperative tissue specimens for culture or if at least 1 intraoperative culture is positive for gram-negative bacteria, plus if there is evidence of infection at the site of prosthesis with presence of a discharging sinus communicating with the joint, operative findings of purulence, or positive laboratory and histopathological test results (Mirra et al. (1976) Clin. Orthop. Relat. Res. 117: 221-240). Several drawbacks are however associated to bacteriological analysis. Conventional detection methods rely on the evidencing of the bacteria on direct examination of the pathological specimen. It is therefore possible that a pathological specimen is not detected by direct microscopic examination of this pathological specimen. Moreover, obtaining pre-operative samples or aspiration liquids for subsequent culture is an invasive procedure which usually requires a surgical procedure carried out under general anesthesia. Secondly, the specificity is often insufficient, since contaminant microorganisms may be isolated. Besides, positive results can be hindered due to the initiation of treatment with antibiotics. Thirdly, no standardized techniques have been established for culturing the samples and interpreting the results from the cultures.
There are currently no other methods for establishing the diagnosis of gram-negative bacteria prosthesis infection. Thus the object of this invention proposes an alternative technique for the diagnosis of the gram-negative prosthetic joint infections. A serological approach based on the antibodies of anti gram-negative bacteria could overcome the drawbacks associated to bacteriological analysis.